A Cooperation-based Approach to Spectrum Reuse

King Abdullah University of Science and Technology and National Science Foundation CCF-0729237

This project examines new paradigms for spectrum reuse based on collaboration between the primary and secondary systems [1]. Traditional cognitive radio systems rely on spectrum sensing techniques to opportunistically reuse unused spectrum bands without any assistance or feedback from the primary system. The lack of feedback from primary systems forces secondary systems (cognitive radios) to be overdesigned, i.e., to take extra protective measures to avoid interfering with the primary, which often limits their practicality. While collaboration can potentially allow both primary and secondary systems to exploit their degrees of freedom more efficiently, new challenges arise beyond those already faced by traditional cognitive radio systems (e.g., interference suppression). In particular, an important requirement in designing those systems is to minimize the required changes to the primary (legacy) systems, in order for this framework to be economically acceptable.
The basic elements of our general architecture are summarized in Figure 1. A secondary transmitter (employing multiple antennas), which can potentially be part of both primary and secondary networks (dual-citizenship), receives feedback from the primary receiver which assists in shaping its beam pattern to avoid interference to the primary. We propose simple and computationally efficient beamforming and beam-nulling algorithms that utilize this feedback to provide significant signal rejection in practical, real-world scenarios [2].